Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $205.86   13.756%   $234.1781   $234.18   $234.20   $234.20  
  Purchase #2 $227.83   6.463%   $242.5547   $242.55   $242.55   $242.60  
  Purchase #3 $248.82   11.382%   $277.1407   $277.14   $277.15   $277.10  
  Purchase #4 $190.55   6.190%   $202.345   $202.35   $202.35   $202.30  
  Purchase #5 $83.76   6.488%   $89.1943   $89.19   $89.20   $89.20  
  Purchase #6 $238.40   5.433%   $251.3523   $251.35   $251.35   $251.40  
  Purchase #7 $179.72   11.291%   $200.0122   $200.01   $200.00   $200.00  
  7 purchase totals = $1,374.94       $1,496.7773   $1,496.77   $1,496.80   $1,496.80